The invention relates to novel compounds derived from α-C-phenyl-N-tert-butylnitrone, to a process for the preparation thereof and to the use thereof for the preparation of medicaments for use in preventing or treating oxidative stress-related diseases.
Pathologies related to oxidative stress and to the formation of oxygen free radical species have been listed by Croos C. E., Arch. Intern. Med. (1987) 107, 526-545 and by Anderson K. M., Ellis G., Bonomi P., Harris J. E., Medical Hypotheses (1999) 52, 53-57.
There are many of them: more than 70 pathologies of this type are mentioned in this list, which includes in particular immune and inflammatory diseases, ischemia-reperfusion syndrome, atherosclerosis, Alzheimer's disease, Parkinson's disease, lesions due to UV radiation and ionizing radiation, certain forms of chemical carcinogenesis and also cell aging.
Oxygen free-radical species and nitrogen free-radical species (ROSs and RNSs) are produced naturally in the organism and the regulation thereof is ensured by certain specialized enzymes such as soluble superoxide dismutase (SODs). The trapping of these extremely reactive free-radical species is essential since they bring about irreversible damage in the cell. While the normal production of these free-radical species is easily regulated by the cell, an overproduction of free radicals related to an external oxidative stress (inflammatory shock, ischemia-reperfusion syndrome, etc.) or a genetic defect (mitochondrial anomalies in particular) leads to rapid cell degradation. It then becomes impossible for the human or animal organism to deal with this large flux of radicals.
There are several defense mechanisms against oxidative stress of the cell, which are capable of operating at various levels of the oxidative cascade. This cascade is generally initiated by the overproduction of superoxide radicals related to a partial reduction in molecular oxygen in the mitochondrion (typical ischemia-reperfusion syndrome). This superoxide radical can undergo dismutation to hydrogen peroxide. These two species, by means of the Fenton reaction, in the presence of ferrous iron, can give hydroxyl radicals which have the particularity of reacting very rapidly and nonspecifically with any of the cell components, such as lipids, DNA or proteins, causing irreversible damage among them, as has been described by Stadtman H. R., Berlett B. S. J. Biol. Chem. (1991) 266, 17201-17211; Floyd R. A. Carcinogenesis (1990) 11, 1447-1450; Gille J. J., Van Berkel C. G., Joenge H. Carcinogenesis (1994) 15, 2695-2699; Halliwell B. Mutat. Res. (1999) 443, 37-52. These free-radical species, by activating certain suicide genes (Bel or p53 genes) through the NF-κB factor, are also responsible for the phenomenon of cell apoptosis which has been described by Siebenlist U., Franzoso G., Brown K., Annu. Rev. Cell. Biol. (1994) 10, 405-455.
Soluble SOD is responsible for converting the superoxide radical to hydrogen peroxide, the latter subsequently being processed by glutathione-dependent peroxidases or catalases.
Other cellular levels of protection against oxidizing agents exist, in particular at the membrane level, which make it possible to limit the oxidation of unsaturated membrane phospholipids. α-Tocopherol and β-carotene are the main examples of lipid antioxidants.
The most promising strategy in the search for a therapy for use in preventing or treating oxidative stress-related diseases consists in intervening as far upstream as possible in this oxidative cascade, in order to prevent, very early on, the damage related to the very high reactivity of the free-radical species.
For this, it has been sought to trap these highly reactive free radicals by means of “spin trap” molecules, among which nitrones appear to be the most effective.
The therapeutic effect of nitrones in the reduction and prevention of damage caused by free radicals in biological systems was demonstrated in 1990 by Oliver C., Starke-Read P., Stadman E., Liu G., Carney J., Floyd R. Proc. Natl. Acad. Sci. USA (1990) 87, 5144-5147.
These authors were able to demonstrate a decrease in the damage caused by cerebral ischemia after injection of α-C-phenyl-N-tert-butylnitrone (PBN) in gerbils. The cerebral ischemia is accompanied by a large increase in the production of free radicals which were trapped by the PBN so as to form spin adducts which are much more stable and therefore much less reactive and toxic. PBN is the spin trap which has been the subject of the most biological studies.
Reference may, for example, be made to Hensley K., Carney J. M., Stewart C. A., Tabatabaie T., Pye Q. N., Floyd R. A. Int. Rev. Neurobiol. (1997) 40, 229-317.
PBN has a high specificity of action in the brain, probably due to its high hydrophobicity, which allows it to cross the blood-brain barrier, as has been shown by Cheng H. Y., Liu T., Feuerstein G., Barone F. C. Free Radic. Biol. Med. (1993) 14, 243-250.
Among the nitrones, the most well known and the most effective are α-C-phenyl-N-tert-butylnitrone (PBN), 5,5-dimethylpyrrolidine-N-oxide (DMPO) and molecules discovered more recently: N-benzylidene-1-diethoxyphosphoryl-1-methylethylamine N-oxide (PBNP) and 5-diethylphosphono-5-methylpyrroline-N-oxide (DEPMPO).
Mention may also be made of a disulfonate derivative of PBN, NXY-059 (disodium 4-[(tert-butylimino]methyl-benzene-1,3-disulfonate N-oxide), which has a neuroprotective activity greater than PBN and which is undergoing pharmacological study and clinical development:    Kuroda S., Tsuchidate R., Smith M. L., Maples K. R., Siesjo B. K. J. Cereb. Blood Flow Metab. (1999) 19, 778-787;    Lees K. R., Sharma A. K., Barer D., Ford G. A., Kostulas V., Cheng Y. F., Odegren T. Stroke (2001) 32, 675-680.
However, none of the molecules mentioned above has a satisfactory efficacy in vivo or ex vivo at low dose, even if their cytotoxic concentration is very high: Almli L. M., Hamrick S. E. G., Koshy A. A., Täuber M. G., Ferriero D. M. Dev. Brain Res. (2001) 132, 121-129; Nakao N., Grasbon-Frodl E. M., Widner H., Brundin P. Neuroscience (1996) 73, 185-200. This lack of efficacy is probably related to poor bioavailability of the drug and to a problem of cell penetration.
There remains therefore the need for a molecule of spin trap type, capable of trapping free radicals, and which is also capable of being conveyed by the human or animal organism to its target at the intracellular level;
In particular, a molecule capable of crossing the cell membrane and, an even greater and more difficult challenge, the mitochondrial membrane in order to enter into the compartment where the superoxide radical is produced.
With this aim, Ouari O., Polidori A., Pucci B., Tordo P., Chalier F. J. Org. Chem. (1999) 64, 3554-3556 and Geromel V., Kadhom N., Cebalos-Picot I., Ouari O., Polidori A., Munnich A., Rötig A., Rustin P. Hum. Mol. Genet. (2001) 10, 1221-1228 have proposed a perfluorocarbon-based amphiphilic derivative of PBN: TA1PBN.

This molecule has been tested on cell lines of fibroblasts suffering from a severe respiratory chain complex V (ATPase) deficiency and has given encouraging results.
However, the synthesis of TA1PBN presents difficulties which render its production on the industrial scale difficult to envision.
International application WO 2004/04982 describes α-C-phenyl-N-tert-butylnitrone derivatives. These spin-trap-type molecules are easy to synthesize and capable of trapping free radicals and they have good bioavailability. One of these compounds, N-[4-(octa-O-acetyllactobionamidomethylene)benzylidene]-N-[1,1-dimethyl-2-(N-octanoyl)amido]ethylamine N-oxide, or LPBNAH, has shown a biological activity greater than that of PBN in oxidative aging tests (B. Poeggeler et al., Journal of Neurochemistry, 2005, 95, 962-973). However, there remains the need for compounds having an even greater activity, and with further increased bioavailability.
The applicant set itself the objective of designing and producing novel molecules, having a spin-trap activity, exhibiting an increased bioavailability compared with the prior art molecules, and the preparation of which is simple and makes it possible to envision production on the industrial scale.